A two year study is proposed to examine the process of diagnostic decision making in child psychiatry, to evaluate it and to explore ways of helping clinicians to make more consistent and reliable diagnoses. Both the reliability and the validity of a diagnostic system such as DSN-III depend on the process by which diagnoses are made. Medicine and psychiatry assume a rational, sequential process in which information is collected and used as a basis for formulating and testing hypotheses about a diagnosis. Empirical studies show that diagnosis in medicine rarely follows this model. The situation in child psychiatry is the subject of this proposal. The proposal investigates the diagnostic process in two ways. 1) Clinical Study: 2 age and sex stratified samples of children coming to urban child psychiatric clinics will be assessed by clinicians with a wide range of training and theoretical persuasions. Sixty cases will be drawn from Western Psychiatric Institute, University of Pittsburgh, and sixty from the Maudsley Hospital, University of London Institute of Psychiatry. Audiotapes of the conferences at which clinicians describe and discuss the case, its diagnosis and treatment, are analyzed using methods derived from recent developments in the cognitive psychology of decision making. Tapes are analyzed in terms of the information units presented, and their use as cues to support or disconfirm clinical hypotheses. The amount and nature of the information used in making the different diagnoses will be examined, together with the effects of child and clinician characteristics and that of using DSM-III vs. ICD-9 as the diagnostic system. 2) Individual Study: Simulated cases will be used to examine the diagnostic process in clinicians working alone, rather than in a group. Verbal protocols of the individual clinicians collecting and evaluating information to make diagnoses in seven specially prepared cases will be tape recorded and analyzed using the same units of analysis as in the clinical studies. The accuracy of diangostic decision making will be evaluated by comparison with a diagnosis based on the judgment of the senior child psychiatrists made six months after assessment, using all available information about treatment and outcome.